1. Field of the Invention
The invention relates to a near-infrared absorption glass, a near-infrared absorption element and a near-infrared absorption filter. More specifically, the invention relates to a near-infrared absorption glass provided with good chemical stability and employed in the near-infrared absorption filter suitable for color sensitivity correction, and a near-infrared absorption element or a near-infrared absorption filter each comprising such glass.
2. Background of the Invention
In recent years, the spectral sensitivity of semiconductor image pickup elements such as CCD and CMOS employed in digital cameras and VTR cameras run from visible to near-infrared range around 1,100 nm. Accordingly, filters absorbing light in the near-infrared range approximating the visual sensitivity of humans are employed to obtain images. Thus filters used for color sensitivity correction become more and more in demand, which in turn poses higher requirements on the near-infrared absorption glass. It is required that the near-infrared absorption glass used for manufacturing such filters possess good transmission property in the visible range.
In prior art, near-infrared absorption glass is manufactured by adding Cu2+ to phosphate glass or fluorophosphate glass. The chemical stability of the phosphate glass is inferior to that of the fluorophosphate glass. Defects such as cracks and white cloud points occur on the surface of the glass upon long-term exposure to high humidity or high temperature.